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Building and tearing down an ice sheet

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  • Building and tearing down an ice sheet

    Background: In the distant past, during a discussion of ice cores, Jorge pointed me to the creation "model" of ice ages: there was only one, and it took 700 years. I did a back-of-the-envelope calculation of the energy imbalance involved, and showed that this was physically impossible. He has, just recently, asked me for a formal summary of the problems with the model. I'll use this thread to work out the issues involved, since i hope it will provide a little insight into scientific reasoning. Plus, if i goof, maybe someone will catch it.

    So, the fact that the creationists accept that an ice age exists means that they accept the indications discovered by scientists of the full extent of the ice sheets during the most recent glacial period. And, really, they're hard to miss; all of Long Island is a giant glacial moraine, and there are plenty of other indications around. The question, however, is what would it take to make these things come and go? Specifically, in this case, we can figure out how much energy was required.

    To do that, we need to figure out how much ice there was. If we take the last glacial maximum (about 20,000 years ago), then the northern hemisphere ice sheets looked like this:
    sheets.JPG

    So, how much ice is there? For the Laurentide, there's a good reference:
    http://onlinelibrary.wiley.com/doi/1...00885/abstract
    26.5 x 10^6 cubic kilometers at the last glacial maximum.

    The Cordilleran has been estimated at 2.9 x􏰁 10^6 cubic km.

    The Innuitan ice sheet, which covered the Canadian archipelago, is estimated at 1.4 x􏰁 10^6 cubic km.
    Both of those from here: http://www.geo.uzh.ch/~chuggel/files...allQSR2002.pdf

    That's 30.8 x 10^6 cubic kilometers and counting. I can't find an academic paper on the rest (Scandinavian, Barents-Kara, and Patagonian). Based on this site:
    http://academic.emporia.edu/aberjame/ice/labs/lab01.htm
    It looks like the majority of the rest of it was in Antarctic sheets, which i've said we're ignoring.

    Is there any way to verify this number? Yes, it's possible to tell what happened to the oceans when all that water was locked away as ice. Ocean levels created new shorelines, and allowed shallow water organisms to grow at greater depths. So we know how much water had to have been in the ice to drop the oceans this much, which provides an independent measure.

    Based on sea level changes, you get an estimate of 52… x 10^6 cubic kilometers of water locked up in ice. That's well above our 31 million cubic km, but we were ignoring a few major contributors. So, as a rough estimate, i think going with 31 million cubic km of ice is reasonable, even if it is extremely favorable to the creationists.

    So, with the ice nailed down, we can do energy calculations. Remember, pretty much all that ice got there because it fell as snow, which means the water must have evaporated at some point. Then it had to be melted. I'll try my hand at the calculations in the next post, then in a 3rd, compare that to solar output.
    "Any sufficiently advanced stupidity is indistinguishable from trolling."

  • #2
    The YEC answer when backed into a corner: It's a miracle.

    Remember YEC must true, evidence be damned.

    K54

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    • #3
      Looking back at the original calculation, I think you made an error in calculating the mass of the ice of around five orders of magnitude; which is going to undermine your comparisons. I'm working through your numbers in the old post and will post a correction there...

      Cheers -- sylas
      Last edited by sylas; 02-24-2015, 08:27 PM.

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      • #4
        Ok, well, i'm starting from scratch, so if there were past mistakes, we'll see if we can fix them.

        In any case, each of those cubic kilometers is a Gigaton, or a billion (10^9) metric tons. Each metric ton is 1,000 kg, and each kg is 1,000 g. That brings us to 10^15 grams of ice per cubic kilometer. We're going with 31 x 10^6 cubic kilometers, which means 3.1 x 10^22 grams of ice. As you say, off by a factor of five from my original calculation. Oops.

        In any case, we need to get that water into the atmosphere so it can fall as snow. The energy of vaporization of water appears to be 2256 Joules/gram. We will unrealistically ignore any of the heat required to up the vaporization rate to have that happen quickly, so it's just 7 x 10^25 Joules. Then, to return to normal conditions, we need to melt it. That takes 333 J/g, which brings us up to 8 x 10^25 J.

        So, hopefully, better math this time. Next up: comparisons with incoming solar radiation.
        "Any sufficiently advanced stupidity is indistinguishable from trolling."

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        • #5
          It seems that some maps indicate that the ice sheets covered more land than the one shown in The Lurch's OP (especially in Eurasia)





          Not sure how accurate they are or what affect they might have on any calculations

          I'm always still in trouble again

          "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
          "Of course, human life begins at fertilization that’s not the argument." --Tassman

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          • #6
            Originally posted by TheLurch View Post
            The energy of vaporization of water appears to be 2256 Joules/gram. We will unrealistically ignore any of the heat required to up the vaporization rate to have that happen quickly, so it's just 7 x 10^25 Joules. Then, to return to normal conditions, we need to melt it. That takes 333 J/g, which brings us up to 8 x 10^25 J.
            There are two issues:
            1) Enthalpy of vaporisation varies with temperature; 2256 J/g is the heat of vaporisation at around 100 deg C, however water generally doesn't evaporate at that temperature (it should be fine for you to assume constant pressure of around 1 atm).

            2) When the vapour condenses back to liquid, it will release heat, so the net change in heat after vaporisation and condensation of the same mass of water could well be 0, and similarly with melting and freezing.

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            • #7
              Originally posted by rogue06 View Post
              It seems that some maps indicate that the ice sheets covered more land than the one shown in The Lurch's OP (especially in Eurasia)





              Not sure how accurate they are or what affect they might have on any calculations
              The larger extent increases albedo for one thing.

              I hope Lurch includes albedo in his ciphering.

              K54

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              • #8
                Originally posted by TheLurch View Post
                In any case, we need to get that water into the atmosphere so it can fall as snow.
                Why do we need the water in the atmosphere? As the ice sheet melted, sea levels rose. The water ends up in the ocean. If you look at energy getting into the atmosphere, you can and SHOULD offset by the release as it comes back down again. It doesn't all get into the atmosphere at the one time. You should stick with heat of fusion, and ignore the energy getting it into the atmosphere. That's 334 J/g.

                [added in edit. Just saw Paprika beat me to it on this point]

                To be honest, I don't think this whole approach is going to be particularly useful or persuasive. There are much better ways for showing problems with creationist time scales.

                (If you do stick with it; you should take into account not only albedo, but also makes some kind of credible calculation of thermal radiation to space from Earth, rather than just having ALL the energy from the Sun go into melting ice. Earth's current emission temperature to space is about 255 K or so; in an ice age it would have be a bit less. 255 K is the temperature to radiate at 240 W/m^2, which is the energy actually absorbed from the sun after albedo is considered. If it was, say 10 degrees colder at the top of the atmosphere that would give 204 W/m^2 (emission varies as the fourth power of absolute temperature) for 36 W/m^2 being absorbed, rather than 343 W/m^2 total from the Sun. There's an order of magnitude for you still with pretty generous conditions. Even so, I just don't think this is going to end up being convincing. Too many technical assumptions being made.)

                Cheers -- sylas
                Last edited by sylas; 02-25-2015, 02:43 PM. Reason: Added emission radation thoughts

                Comment


                • #9
                  Originally posted by sylas View Post
                  Why do we need the water in the atmosphere? As the ice sheet melted, sea levels rose. The water ends up in the ocean. If you look at energy getting into the atmosphere, you can and SHOULD offset by the release as it comes back down again. It doesn't all get into the atmosphere at the one time. You should stick with heat of fusion, and ignore the energy getting it into the atmosphere. That's 334 J/g.

                  [added in edit. Just saw Paprika beat me to it on this point]

                  To be honest, I don't think this whole approach is going to be particularly useful or persuasive. There are much better ways for showing problems with creationist time scales.

                  (If you do stick with it; you should take into account not only albedo, but also makes some kind of credible calculation of thermal radiation to space from Earth, rather than just having ALL the energy from the Sun go into melting ice. Earth's current emission temperature to space is about 255 K or so; in an ice age it would have be a bit less. 255 K is the temperature to radiate at 240 W/m^2, which is the energy actually absorbed from the sun after albedo is considered. If it was, say 10 degrees colder at the top of the atmosphere that would give 204 W/m^2 (emission varies as the fourth power of absolute temperature) for 36 W/m^2 being absorbed, rather than 343 W/m^2 total from the Sun. There's an order of magnitude for you still with pretty generous conditions. Even so, I just don't think this is going to end up being convincing. Too many technical assumptions being made.)

                  Cheers -- sylas
                  with an average glacial thickness of 3-4 km, attained after 300 years, I would think an average annual cumulative snowfall (after subtracting out any summer melting) of 10 to 13 meters (33 to 42 ft) would be sufficient to ground the YEC approach to the problem ...



                  Jim
                  He will reply, ‘Truly I tell you, whatever you did not do for one of the least of these, you did not do for me."

                  "So in everything, do to others what you would have them do to you, for this sums up the Law and the Prophets"

                  Comment


                  • #10
                    Originally posted by klaus54 View Post
                    The YEC answer when backed into a corner: It's a miracle.

                    Remember YEC must true, evidence be damned.

                    K54
                    This is why going to lots of trouble establishing the physical impossibility of countless implications of YEC doctrine is a waste of time. The YEC god really CAN make a rock so heavy he can't lift it, even though he can lift it easily. He can do anything.

                    Comment


                    • #11
                      Originally posted by phank View Post
                      This is why going to lots of trouble establishing the physical impossibility of countless implications of YEC doctrine is a waste of time. The YEC god really CAN make a rock so heavy he can't lift it, even though he can lift it easily. He can do anything.
                      But they also crow over (physical) evidence they think might support their "model".

                      It's a heads-I-win, tails-you-lose scenario. (I learned that from the Senor Porgie.)

                      Comment


                      • #12
                        Originally posted by oxmixmudd View Post
                        with an average glacial thickness of 3-4 km, attained after 300 years, I would think an average annual cumulative snowfall (after subtracting out any summer melting) of 10 to 13 meters (33 to 42 ft) would be sufficient to ground the YEC approach to the problem ...



                        Jim
                        So it for the first 350 years Earth was so cold that 2km thickness of glacial ice could form (BTW, glacial ice is not just old snow), cold enough to do the unmentionable to a brass monkey. Then in few years Earth warmed fast enough to overcome the albedo and melt enough ice to raise mean sea level 70 meters within another 350 years.

                        Sounds like a cogent model to me.

                        K54

                        Comment


                        • #13
                          Originally posted by klaus54 View Post
                          So it for the first 350 years Earth was so cold that 2km thickness of glacial ice could form (BTW, glacial ice is not just old snow), cold enough to do the unmentionable to a brass monkey. Then in few years Earth warmed fast enough to overcome the albedo and melt enough ice to raise mean sea level 70 meters within another 350 years.

                          Sounds like a cogent model to me.

                          K54
                          yes, I figured I'd save the fact the snow compresses significantly to form the ice sheet for someone who thinks 40 ft of snowfall per year remaining after any summer melt for 300 years in a row over all of canada and northern europe made sense.

                          Jim
                          He will reply, ‘Truly I tell you, whatever you did not do for one of the least of these, you did not do for me."

                          "So in everything, do to others what you would have them do to you, for this sums up the Law and the Prophets"

                          Comment


                          • #14
                            Originally posted by oxmixmudd View Post
                            yes, I figured I'd save the fact the snow compresses significantly to form the ice sheet for someone who thinks 40 ft of snowfall per year remaining after any summer melt for 300 years in a row over all of canada and northern europe made sense.

                            Jim
                            There's also the issue of the cycle of glacials and interglacials in the Pleistocene/Holocene.

                            Originally posted by From cited webpage
                            ...Within the past 750,000 years, scientists know that there have been eight Ice Age cycles, separated by warmer periods called interglacial periods. Currently, the Earth is nearing the end of an interglacial, meaning that another Ice Age is due in a few thousand years. This is part of the normal climate variation cycle....
                            Source: http://nsidc.org/cryosphere/glaciers/questions/what.html


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